Converging chamber saturator with removable insert

ABSTRACT

A saturator of the type comprising a chamber situated between a chamber defining element and a mandrel, in which a web is moved between the chamber defining element and the mandrel to impregnate the web with a saturant contained in the chamber includes at least one saturant delivery port which extends across substantially the entire width of the chamber or the entire width of one of the saturating zones if the chamber defines a plurality of saturating zones. In this way, uniformity of saturation across the chamber is improved. An insert is removably mounted to the chamber defining element such that a surface of the insert defines a wall of the chamber.

CROSS REFERENCE TO RELATED APPLICATION

This is a division of Ser. No. 07/073,516, filed July 15, 1987, now U.S.Pat. No. 4,849,261, which is a continuation-in-part of application Ser.No. 06/883,550 filed July 9, 1986, now U.S. Pat. No. 4,702,943.

BACKGROUND OF THE INVENTION

The present invention relates to saturators for impregnating a substratewith a saturant.

Saturators have been used for some time to impregnate substrates such aswebs of paper with varying amounts of saturants. By properly selectingthe amount and type of saturant to provide the desired characteristicsto the substrate, saturators can be used to enhance the physicalcharacteristics, and therefore the value, of the substrate.

For example, one valuable saturant is sodium silicate. When high levelsof sodium silicate are added to a paper web, the paper can be made fireresistant and can be given much improved structural strength. However,such highly impregnated paper can be difficult to fold or crease inconventional paper processing machines. It therefore would beadvantageous to impregnate a paper web with sodium silicate only atselected portions of the web. For example, if a paper web were to beused to form a box in which stacking strength were an importantconsideration, it would often be advantageous to apply sodium silicateonly to the sidewalls of the box, and not to the top and bottom panels,which must be folded in use.

As another example, containers such as beer cases are subjected tounusual wear patterns. The tops and bottoms of the cans within the caseact as cookie cutters during transportation and can severely damageeither the printing on or the actual structure of the top and bottompanels of the case. If sodium silicate were applied to the top andbottom panels, this cookie cutter effect could be resisted effectively.In this example, however, there is no need to apply sodium silicate tothe sidewalls, and it would save the cost of materials if the saturantcould be placed on only the top and bottom panels and not the sidewallsof the case.

In spite of the important advantages that selective saturation wouldprovide in the examples described above, the applicant is unaware of anysaturator that performs this function. The saturator described in MenserU.S. Pat. No. 4,588,616 is an extremely effective device which can beused to saturate substrates with a range of saturants at both relativelylow and extremely high add-on weights. Similarly, U.S. Pat. No.2,721,144 describes another type of saturator used in the past. However,neither of these saturators is provided with means for selectivelyimpregnating only portions of the web with the saturant.

In the past, stencils have been used with a variety of surfaceapplicators for liquids of various types. However, such stencils havenot, to the knowledge of the applicant, been used with saturators.Instead, stencils have typically been used with applicators which applyliquid to the surface of a web without substantial impregnation.Examples of such applicators are spray devices (Smith U.S. Pat. No.3,088,859); extruders (Sorg U.S. Pat. No. 2,904,448); roller applicators(Holdsworth U.S. Pat. No. 2,056,274); and spreaders (Hannington U.S.Pat. No. 1,546,834). Such applicators differ significantly fromsaturators in that they apply a liquid to the surface of the substratewithout specific pressure to force the applied liquid into theinterstices of the substrate and therefore do not provide deepimpregnation as does a saturator.

SUMMARY OF THE INVENTION

The present invention is directed to an improved saturator of the typethat comprises a pair of chamber defining elements that form aconverging saturating chamber therebetween, and means for moving a webthrough the saturation chamber along a translation axis from theentrance region to the exit region, wherein the chamber converges from arelatively deeper entrance region to a relatively shallower exit region,and the chamber is shaped to pressurize saturaute in the exit region ascompared with the entrance region. According to this invention at leastone insert is provided, along with means for removably mounting theinsert to one of the two chamber defining elements such that the insertforms a surface of the converging chamber.

In the embodiments described below, a saturator of the type comprisingmeans for defining a chamber for containing a pressurized saturanttherein, and means for moving a web through the chamber to bring a firstside of the web into contact with the pressurized saturant to cause thesaturant to impregnate the web, is provided with a stencil having atleast one impermeable region shaped to cover less than the entire web.Means are provided for passing the stencil through the chamber at thesame speed as the web with the stencil juxtaposed against the first sideof the web, such that portions of the web aligned with the at least oneimpermeable region are not impregnated with the saturant, while other,exposed portions of the web are impregnated with the saturant.

In these embodiments, a saturant is selectively applied only to apatterned portion of a web with a saturator of the type comprising meansfor defining a chamber for containing a pressurized saturant therein,and means for moving the web through the chamber to bring a first sideof the web into contact with the pressurized saturant to cause thesaturant to impregnate the web. This method comprises the steps of (1)providing a stencil having at least one impermeable region shaped tocover less than the entire web, and (2) passing the stencil through thechamber at the same speed as the web with the stencil juxtaposed againstthe first side of the web, such that the portions of the web alignedwith the at least one impermeable region are not impregnated with thesaturant, and other, exposed portions of the web are impregnated withthe saturant.

As described in detail below, this method provides important advantagesin that it allows only selected patterned portions of a web to beimpregnated with the saturant. By applying the saturant only where it isneeded on the web, the cost of saturant is reduced, and the end productcan actually be improved. For example, impregnation of the web can beavoided in regions where the web will be creased or folded, such thatthe saturant does not interfere with such subsequent processingoperations. As another example, saturant can be kept out of contact withpatterned portions of the web which will subsequently be printed in theevent a saturant is used with detracts from the clarity or colortrueness of the printing operation.

The invention itself, together with further objects and attendantadvantages, will best be understood by reference to the followingdetailed description, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view through a pattern-forming saturator.

FIGS. 2a, 2b and 2c are partial plan views of alternative stencilssuitable for use in the saturator of FIG. 1.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1.

FIG. 4 is a perspective view of a saturator which incorporates apreferred embodiment of this invention.

FIG. 5 is an exploded perspective view of components of the saturator ofFIG. 4.

FIG. 6 is a sectional view taken along line 6--6 of FIG. 5.

FIG. 7 is a fragmentary perspective view of portions of a variant of theembodiment of FIG. 4, which incorporates another preferred embodiment ofthis invention.

FIG. 7a is a sectional view taken along line 7a--7a of FIG. 7.

FIG. 7b is a sectional view taken along line 7b--7b of FIG. 7.

FIG. 8 is a cross-sectional view of a saturator which incorporatesanother preferred embodiment of this invention.

FIG. 9 is a fragmentary view taken along line 9--9 of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 shows a cross sectional view of apattern-forming saturator 10. This saturator 10 includes a mandrel 12which is mounted for powered rotation about an axis defined by a shaft14. Typically, the mandrel 12 is formed of a steel shell having a lengthat least as great as the widest web to be processed. The mandrel 12 ismounted for rotation adjacent to a chamber defining element 16 whichextends along the length of the mandrel 12. This chamber definingelement 16 defines a chamber 18 between the element 16 and the mandrel12. This chamber 18 is characterized by an entrance region 20 and anexit region 22. The chamber 18 is deeper in the entrance region 20 thanin the exit region 22, and preferably the chamber 18 tapers in depth ina gradual and progressive manner.

A supply port 24 supplies a liquid saturant, such as an aqueous sodiumsilicate solution, to the chamber 18. If desired, the saturant can besupplied to the chamber 18 under pressure via the supply port 24, oralternately, the self-pressurizing features of the saturator 10described below can be used to create the desired pressure of saturantwithin the chamber 18. A plurality of spring seals 26 formed of asuitable spring steel are mounted to the chamber defining element 16adjacent to the entrance region 20 to impede the flow of saturant out ofthe chamber 18. An entrance roll 30 and an exit roll 32 are mounted forrotation adjacent to respective sides of the chamber defining element16.

The features of the saturator 10 described above are substantiallyidentical to those described in Menser U.S. Pat. No. 4,588,616. Thispatent is hereby incorporated by reference for its detailed teaching ofthe structure of the saturator 10, and in particular for its teaching ofthe geometry of the converging chamber 18. As explained in detail in theMenser patent, a web 40 is passed between the mandrel 12 and the chamberdefining element 16, such that the web 40 is moved through the chamber18 from the entrance region 20 to the exit region 22, carried by therotation of the mandrel 12. Movement of the web 40 through theconverging chamber 18 pressurizes the saturant within the chamber 18,thereby forcing the saturant to impregnate voids or pores in the web 40.After the web 40 has been impregnated with the saturant, it leaves theconverging chamber 18 via the exit roll 32 and typically passes to anoven (not shown) where volatile components of the saturant are removed.As one example of a suitable saturant, aqueous solutions of sodiumsilicate as described in the Menser patent can be used.

As pointed out below, the arrangement of the supply port 24 can createlocalized variations in the amount of saturant impregnated into the web.Such variations can result from non-uniformity in the velocity of thesaturant, which in turn result from the fact that the supply port 24extends over only a small part of the width of the chamber.

A stencil 50 is provided to prevent patterned portions of the web 40from coming into contact with the saturant in the chamber 18. Thisstencil 50 includes both impermeable regions 52 and permeable regions54. As shown in FIG. 1, the stencil 50 preferably moves in a closed loopabout the entrance roll 30, the exit roll 32, and idler rolls 56, suchthat the stencil 50 is in intimate contact with the side of the web 40facing the chamber defining element 16. In the permeable regions 54 ofthe stencil 50, the saturant comes into contact with the web 40 and theweb 40 is impregnated with saturant in the conventional manner. In theimpermeable regions 52 of the stencil 50 the saturant is prevented fromcoming into contact with the web 40.

The stencil 50 preferably moves at the same linear speed as the web 40,such that there is no relative movement between the web 40 and thestencil 50. In this embodiment, this desired result is obtained in thatthe web 40 frictionally engages and drives the stencil 50. Of course, inalternate embodiments it may be preferable to provide an active drivesystem for the stencil 50 to synchronize the linear speed of the stencil50 with the web 40.

FIGS. 2a, 2b and 2c provide partial plan views of three exemplarystencils 50a, 50b and 50c that may be used with the pattern-formingsaturator 10 of FIG. 1. The first example of FIG. 2a includes twolateral bands 58, each having a substantially constant width, and eachpositioned to protect a respective lateral portion of the web 40. Thus,the impermeable regions 52a of the stencil 50a cover the two lateraledges of the web 40, and the permeable region 54a allows the centralregion of the web 40 to be impregnated with the saturant.

FIG. 2b shows an alternative stencil 50b which includes one central band60 having a generally uniform width. This central band 60 is positionedto insure that the impermeable region 52b is entered on the web 40 toprevent the central portion of the web 40 from being impregnated withthe saturant. The lateral edges of the web 40 are aligned with thepermeable regions 54b of the stencil 50b, and are impregnated withsaturant as the web 40 moves through the chamber 18.

FIG. 2c shows a third stencil 50c which comprises a band that extendsover the full width of the web 40. This band defines discreet permeableregions 54c, each completely surrounded by the band which forms theimpermeable region 52c. The stencil 50c insures that the saturator 10impregnates the web with the saturant only in isolated regions alignedwith the discrete permeable regions 54c.

The saturator 10 provides high saturant pressures in the exit region 22.In order to reduce the leakage of saturant out the exit region 22, thesaturator 10 includes an exit seal 70 which is best shown in FIG. 3. InFIG. 3 the stencil 50a of FIG. 2a is shown for illustrative purposes,including the two lateral bands 58. The exit seal 70 defines recesses 72positioned to receive the lateral bands 58. These recesses 72 areseparated by a raised area 74. The depth of each of the recesses 72 issubstantially equal to the thickness of the lateral bands 58. Thenotched profile of the exit seal 70 defined by the recesses 72 and theraised area 74 seals the exit region 22 to minimize leakage of saturantpast the exit seal 70.

In use, the web 40 is passed through the chamber 18 between the stencil50 and the mandrel 12 such that regions of the web 40 aligned with theimpermeable regions 52 of the stencil 50 are protected from contact withthe saturant in the chamber 18, while regions of the web 40 aligned withthe permeable regions 54 of the stencil 50 are impregnated with thesaturant in the conventional manner. In this way, the saturant isapplied only to the desired portions of the web 40, thereby providingimportant advantages in terms of both utility and economy. Utility isimproved in that the saturant can be kept out of contact with undesiredregions of the web, as for example regions of the web that are to beprinted or otherwise processed in a manner incompatible with thesaturant. Economy is improved in that by applying the saturant only tothe desired portions of the web 40, the usage and therefore cost of thesaturant needed to process a particular web 40 are reduced.

The saturator of FIGS. 4-6 is similar to the saturator 10 in that itincludes a rotatable mandrel 112 and a stationary chamber definingelement 116. A converging chamber 118 similar to the chamber 18 of thefirst preferred embodiment is defined between the element 116 and themandrel 112. This converging chamber 118 defines a relatively deepentrance region 120 and a relatively shallow exit region 122, asdescribed above. Saturant is supplied to the converging chamber 118through a manifold 124. In alternate embodiments, the saturant can besupplied via the manifold 124 under a wide range of pressures, dependingupon the desired degree of saturation and other parameters of thesaturation process.

The chamber defining element 116 is mounted on a frame 134 which is, inturn, pivotably mounted for rotation about a pivot axis 136. Thismounting arrangement for the element 116 provides a number of importantadvantages. First, the frame 134 can readily be pivoted away from themandrel 112. This simplifies cleaning operations and it allows theelement 116 to be moved briefly away from the mandrel 112 when necessaryto pass a splice on the web 140. Furthermore, this arrangement allowsthe depth of the converging chamber 118 at the entrance and exit regions120, 122 to be adjusted substantially independently of one another. Bymoving the pivot axis 136 toward and away from the mandrel 112, thedepth of the entrance region 120 can be precisely adjusted, withoutsubstantially altering the depth of the chamber 118 at the exit region122. Similarly, by providing a precisely adjustable stop surface nearthe exit region 122, the frame 134 can be positioned so as to obtain thedesired depth at the exit region 122 without significantly altering thedepth at the entrance region 120.

The web 140 is moved through the converging chamber 118 by rotation ofthe mandrel 112. A stencil 150 is brought into contact with the surfaceof the web 140 adjacent to the saturant in the converging chamber 118,and friction between the stencil 150 and the web 140 insures that thestencil 150 moves at the same linear speed as the web 140, withoutslippage between the stencil 150 and the web 140. If desired, anauxiliary drive system can be provided for the stencil 150 to reducedrag on the web 140.

The stencil 150 includes a number of parallel bands spaced across thelength of the mandrel 112. The bands themselves form impermeable regions152 which prevent saturant from reaching the web 140. The regionsbetween the bands act as permeable regions 154 which allow the saturantto reach and impregnate the web 140. FIG. 4 shows a stencil cleaningsystem 156 which removes saturant from the stencil 150. A variety ofapproaches can be used in the system 156 to clean the stencil, such aschemical baths, mechanical brushes, scrapers, and the like.

As best shown in FIGS. 5 and 6, an insert 180 is mounted to the element116 such that it is the insert 180 that defines the interior wall of theconverging chamber 118. This insert 180 is provided with a plurality ofspaced parallel grooves 182, each sized to receive a respective one ofthe bands of the stencil 150. The grooves 182 are separated by raisedareas 184. As shown in FIG. 5, the grooves 182 increase in depth as theyapproach the trailing edge 190 of the insert 180, and at the trailingedge 190 the grooves have a depth equal to the thickness of the bandssuch that the raised areas 184 directly contact the web 140.

The insert 180 can be formed of any suitable material and it isanticipated that a range of plastics and metals will be found suitable.In this embodiment, the converging chamber 118 is shaped much like theconverging chamber 18 shown in FIG. 1, and the leading edge 186 of theinsert 180 is positioned to abut a retainer 158 mounted to the element116 near the entrance region 120.

The presently preferred arrangement for mounting the insert 180 in placeis best shown in FIGS. 5 and 6. The element 116 defines a channel 160which extends parallel to the mandrel 112. This channel 160 definesspaced parallel slots 162 which extend along the length of the channel160, and the channel 160 is connected to the manifold 124 through aplurality of spaced ports 126. The retainer 158 defines flanges 164sized to fit within the slots 162 to hold the retainer 158 in place onthe element 116. The retainer 158 define a lip 166 which fits over theleading edge 186 of the insert 180 and holds it in place. A plurality ofopenings 168 are defined by the retainer 158 to allow saturant to flowfrom the channel 160 to the converging chamber 118 into the regionsbetween the bands of the stencil 150. Thus, the retainer 158 both holdsthe leading edge 186 of the insert 180 in place and distributes saturantinto the chamber 118.

As shown in FIG. 5, the openings 168 are substantially equal in width tothe raised areas 184 which define the saturation zones. This aspect ofthe invention reduces non-uniformities in the amount of saturant addedto the web across the width of each of the saturation zones. Suchnon-uniformities have been recognized as a problem in saturators inwhich saturant flows into the chamber through relatively small, widelyspaced ports. This aspect of the invention can be used in saturatorswhich do not employ stencils, in which case one of the openings 168 ispreferably sized to extend completely across the entire width of theweb. In this way uniform saturation across the entire width of the webcan be obtained. Of course, in such embodiments which do not employstencils, the insert 180 is preferably uniform across its width, and nogrooves 182 are provided.

The trailing edge 180 of the insert 180 defines an array of protrudingfingers 192 and these fingers 192 are captured in place by respectiveopenings 194 in a plate 196. The plate 196 is in turn removably securedto the element 116, as for example by screws 198.

The insert 180 acts as a seal by receiving the bands of the stencil 150within the grooves 182. In effect, the insert 180 becomes a portion ofone wall of the converging chamber 118, and this wall is contoured toreceive the stencil 150. In this way, the raised areas 184 can bepositioned as close to the web 140 as desired to obtain the necessarysealing action and to develop the desired pressure within the convergingchamber 118. Of course, in alternate embodiments, the grooves 182 canactually be formed in the element 116, thereby eliminating the need fora separate insert. However, the insert 180 provides importantadvantages, in that it allows the element 116 to be readily adapted todiffering stencils, simply by replacing the insert 180. If necessary,the retainer 158 can readily be removed and replaced as well.

FIGS. 7, 7a and 7b relate to a preferred embodiment which is similar tothe embodiment of FIGS. 4-6. The key difference is that in theembodiment of FIGS. 7-7b the insert, retainer and plate are all formedof separate, modular components. In FIGS. 7-7b the same referencenumerals are used as in FIGS. 4-6 for corresponding elements, exceptthat the reference numerals of FIGS. 7-7b are primed. Except asindicated below, these embodiments are identical.

In the embodiment of FIGS. 7-7b , the insert 180' is composed ofmultiple parallel, spaced elements, each of which defines a respectiveleading and trailing edge 186', 190'. The leading edges 186' are held inplace by retainers 158', and the trailing edges 190' are held in placeby plates 196', all as described above in connection with FIGS. 5-6. Thebands of the stencil (not shown) are sized and positioned to movebetween the inserts 180'. Thus, the inserts 180' of FIG. 7 correspond infunction to the raised areas 184 of FIG. 5 and the regions between theinserts 180' of FIG. 7 correspond to the grooves 182 of FIG. 5. Theretainers 158' are separated by spacers 170' which slide in the slots162' and block the flow of saturant out of the channel 160' in theregion between the retainers 158'.

The embodiment of FIGS. 7-7b is modular in construction, and it allows asmall number of inserts 180', retainers 158', spacers 170' and plates196' to be combined as desired to accommodate a large variety ofspacings and widths of the bands of the stencil. Preferably the inserts180' are equal in width to the corresponding retainers 158' and plates196'.

FIGS. 8 and 9 relate to another preferred embodiment 200 of thisinvention. This embodiment 200 differs significantly from the previousembodiments in that neither of the two chamber defining elements 212,214moves relative to the other in operation. Rather, each of the elements212,214 is rigidly held in position by a frame (not shown). The twoelements 212,214 define a converging chamber 216 therebetween. Thisconverging chamber 216 includes a relatively deep entrance region 218and a relatively shallow exit region 20. The elements 212,214 define anextended exit region 222 which provides an important sealing function asdescribed below. Saturant is supplied to the converging chamber 216 viaa supply port 224, which preferably extends completely across the widthof the web 240 to provide uniform saturation in the saturation zones asdescribed above.

The embodiment 200 includes upper and lower belts 230,232, each of whichis rotated by a respective drive system 234,236 such that the two belts232,234 move between the elements 212,214 at the same speed, therebycarrying the web 240 through the converging chamber 216. Preferably,these belts 230,232 are formed of an impermeable material such asstainless steel, and suitable lubricants are provided between the belts230,232 and the chamber defining elements 212,214.

In addition, a closed loop stencil 250 is also passed through theconverging chamber 216 positioned immediately adjacent to the web 240.This stencil 250 is moved at the same linear speed as the web 240,carried along by friction between the stencil 250 and the web 240. Astencil cleaning system 256 as described above is provided to removesaturant from the stencil 250.

As best shown in FIG. 9, in this embodiment the stencil 250 comprises aplurality of impermeable regions 252, each made up of a respective oneof three parallel bands, and a plurality of permeable regions 254positioned between the bands. In addition, the bands are interconnectedby semi-permeable regions 253. In this embodiment, the semi-permeableregions 253 are formed of an impermeable sheet which defines a pluralityof small openings. These openings allow some saturant to flow into theweb 240. However, the flow of saturant into those portions of the web240 aligned with the semi-permeable regions 253 is reduced as comparedwith the flow of saturant into those portions of the web 240 alignedwith the permeable regions 254. Thus, the resulting saturated web 240 isdevoid of saturant in certain portions aligned with the impermeableregions 252, is saturated to a greater extent in portions aligned withthe permeable regions 254, and is saturated to a lesser extent inportions aligned with the semi-permeable regions 253. This can be ofgreat advantage, for example, in conjunction with containers which areto have a high degree of saturation in the sidewalls, a low degree ofsaturation in the bend lines between adjacent sidewalls, andsubstantially no saturation in the end panels. The stencil 250 of FIG. 7is suitable for such an application. The precise size and spacing of theopenings of the semi-permeable regions 253 can be varied widely.However, in many cases it is preferable to have the openingssufficiently closely spaced such that the saturant is distributed acrossthe entire portion of the web 240 aligned with the semi-permeableregions 253, rather than being localized into individual spots.

The extended exit 222 shown in FIG. 6 defines a chamber depth which issubstantially equal to the sum of the thicknesses of the belts 230,232,the web 240, and the stencil 250. The length of the extended exit 222along the direction of motion of the web 240 is preferably greater thanthe separation between two adjacent semi-permeable regions 253 along thedirection of motion of the stencil 250. In this way, the pressure dropacross a single one of the semi-permeable regions 253 is reduced, andthe tendency to stretch the stencil 250 is reduced as well.

Of course, it should be understood that a wide range of changes andmodifications can be made to the preferred embodiments described above.For example, it is not necessary in all embodiments that a convergingchamber be used. Rather, a non-converging chamber of the type shown inPenley U.S. Pat. No. 2,711,032 is well suited for some applications.Furthermore, the particular geometry of the stencil can readily beadapted for the particular application. In the preferred embodimentdescribed above, the stencil is formed of a sheet of stainless steel.However, other materials can be used as appropriate for the particularapplication.

It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting, and that it be understoodthat it is the following claims, including all equivalents, which areintended to define the scope of this invention.

I claim:
 1. In a saturator of the type comprising two opposed elementswhich define a converging saturating chamber therebetween, which chamberconverges from a relatively deeper entrance region to a relativelyshallower exit region, and means for moving a web through the saturationchamber along a translation axis from the entrance region to the exitregion, wherein the chamber is shaped to pressurize saturant in thechamber, the improvement comprising:at least one insert; means forremovably mounting the insert to one of the two opposed elements suchthat the insert forms a surface of the converging chamber and extendsfrom the exit region at least partially towards the entrance region; andmeans, included in the moving means, for defining at least one wall ofthe chamber having a surface movable in the same general direction asthe web is movable.
 2. The invention of claim 1 wherein the web definesa width transverse to the translation axis, and wherein the insertextends over at least part of the width of the web.
 3. The invention ofclaim 1 wherein the insert defines at least one stencil receiving grooveextending parallel to the translation axis.
 4. The invention of claim 1wherein the mounting means comprises a plate removably mounted to saidone of the two opposed elements, and means for releasably engaging theinsert with the plate.
 5. The invention of claim 4 wherein thereleasably engaging means comprising an array of projections on theinsert and an array of openings in the plate, each opening sized toreceive a respective one of the projections.
 6. The invention of claim 1wherein the mounting means comprises a retainer mounted to said one ofthe two opposed elements, wherein said retainer defines a flange,wherein said insert defines a leading edge and a trailing edge, andwherein said leading edge is removably received under said flange. 7.The invention of claim 6 wherein the other of said two opposed elementscomprises a rotatable mandrel.
 8. In a saturator of the type comprisingtwo opposed elements which define a converging saturating chambertherebetween, which chamber converges from a relatively deeper entranceregion to a relatively shallower exit region, and means for moving a webthrough the saturation chamber along a translation axis from theentrance region to the exit region, wherein the chamber is shaped topressurize saturant in the chamber, the improvement comprising:at leastone insert; and means for removably mounting the insert to one of thetwo opposed elements such that the insert forms a surface of theconverging chamber; wherein the insert defines at least one stencilreceiving groove extending parallel to the translation axis.
 9. Theinvention of claim 8 wherein the insert extends from the exit region atleast partially towards the entrance region.
 10. The invention of claim8 wherein the means for removably attaching the insert to the chamberdefining element comprising an array of protruding elements defined bythe insert and a support member having a plurality of openings shapedand positioned to receive the protruding elements of the insert inplace.
 11. The invention of claim 10 wherein the means for removablyattaching the insert to the chamber defining element further comprisesmeans for removably mounting the support member to the chamber definingelement.
 12. In a saturator of the type comprising two opposed elementswhich define a converging saturating chamber therebetween, which chamberconverges from a relatively deeper entrance region to a relativelyshallower exit region, and means for moving a web through the saturationchamber along a translation axis from the entrance region to the exitregion, wherein the chamber is shaped to pressurize saturant in thechamber, the improvement comprising:at least one insert; and means forremovably mounting the insert to one of the two opposed elements suchthat the insert forms a surface of the converging chamber; wherein themounting means comprises a plate removably mounted to said one of thetwo opposed elements, and means for releasably engaging the insert withthe plate.
 13. The invention of claim 12 wherein the releasably engagingmeans comprises an array of projections on the insert and an array ofopenings in the plate, each opening sized to receive a respective one ofthe projections.